Welding apparatus



Patented July 22, 1941 WELDING APPARATUS Colby W. Steward, WestSpringfield, Mass., assignor to Westinghouse Electric is ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationJanuary 4, 1939, Serial No. 249,188

9 Claims.

My invention relates, generally, to welding apparatus, and it hasparticular reference to a control system for fluid pressure operatedwelding apparatus.

In general, it is an object of my invention to provide for controllingin a simple and efllcient manner the sequence of operations in fluidpressure operated welding apparatus.

More specifically it is an object of my invention to controlautomatically the sequence of the application of electrode pressure andthe energization of the welding circuit in fluid pressure actuated seamor spot welding apparatus, so as to prevent energization of the weldingcircuit unless a predetermined differential of fluid pressure existsbetween particular points in the fluid pressure system.

Another object of my invention is to provide fluid pressure actuatedrelay means, responsive to a differential in pressure between two pointsin the fluid pressure system, for eifecting the energization anddeenergization of the welding circuit in fluid pressure actuated weldingapparatus in accordance with the application of fluid pressure to, andits removal from the electrode actuating means.

A further object of my invention is to provide for coordinating theconnection of the welding pressure actuated welding apparatus, so as toprovide for single or repeated operations thereof, prevent energizationof the electrodes before the proper electrode pressure has been applied,and prevent accidental reduction of the electrode pressure before thedisconnection of the welding electrodes from the source.

Other objects will, in part, be obvious and will, in part, appearhereinafter.

In practicing a preferred embodiment of my invention, the energizationof the welding electrodes of fluid pressure operated spot or seamwelding apparatus from a source of power may be controlled by providingdifferential fluid pressure relays connected between the source of fluidpressure and the cylinder of the fluid pressure electrode actuatingmeans. By suitably designing the differential pressure relays so thatthey operate only upon the existenceof a predetermined differential inpressure between the fluid pressure source and the cylinder of theelectrode actuating means, suitable timing means may be energizedthereby in accordance with a predetermined condition of electrodepressure to effect the connection of the electrodes to the source ofpower for a predetermined interval of time. In this manner the sequenceof welding operations may be readily controlled, energization of theelectrodes being prevented until a suitable condition of electrodepressure is first attained, and their deenergization being effectedprior to the reduction of such pressure. By suitably controlling therate of flow of fluid pressure between the cylinder of theelectrode'actuating means and one of the differential pressure relaysthrough the use of suitable valve means, and connecting the relay tocontrol the application of fluid pressure to the electrode actuatingmeans, successive applications of fluid pressure thereto can beprevented until the differential between the ifluid pressures applied tothe relay has reached the predetermined operating value, so that theperiod of deenergization of the welding electrodes between repeatedoperations may be effectively controlled, thus preventing successiveenergizations of the welding electrodes before the lapse of a suitablepredetermined interval of time. This feature is often desirable inconnection with high speed welding operations so as to permit the properfeeding of the work bein welded, between successive welding operations.

For a more complete understanding of the nature and scope of myinvention reference may be had to the following detailed description,taken in connection with the accompanying drawing, in which the singlefigure represents diagrammatically a fluid pressure operated weldingsystem embodying a preferred form of my invention.

The reference numeral Ill in the single flgure of the drawing denotesgenerally a transformer having a primary winding it connected to asuitable source of alternating-current power it through the contactmembers lid and lib of a line switch It, and a secondary winding I8,connected to a welding circuit comprising, for example, relativelymovable electrodes l9 and 20 of a welding machine for performing awelding operation on work 22, which may be positioned therebetween,

The electrode 2| may be supported in any well-known manner so as to bemovable relative to the electrode ll, being for example, operativelyconnected to fluid pressure actuating means such as the piston 24, whichis siidably positioned within a cylinder 16. In order to suitablycontrol the movement of the electrode 20, a reversible fluid pressurevalve 2| may be provided for controlling the connection of the c'ylinder26 to a suitable source of fluid pressure I.

As illustrated, the valve 28 may comprise a casing 3i having a supplychamber 32 connected to the source of fluid pressure by means of aconduit 34, associated inlet chambers 36 and 38 positioned on each sideof the supply chamber 32 and connected to the cylinder 26 at theopposite ends thereof by conduits 40 and 42, respectively, for admittingfluid pressure to the cylinder 26 on either side of the piston 2t, andexhaust chambers 44 and 46 for connecting the conduits 40 and 42,respectively, to the atmosphere to effect the removal of the fluidpressure from either side of the piston 24. A plurality of valve members41, 48, 49 and 50, for controlling the application of fluid pressure tothe fluid pressure actuating cylinder 26 from the source 30, may bepositioned on a movable stern having an operatively connected armature52 which is actuated by the energization of an associated operatingwinding "53, and which is normally retained in the position shown bymeans such as the spring 54.

Any suitable timing means such, for example, as indicated generally bythe reference numeral 60, may be provided for controlling the operationof the line switch l6, so as to control the energization anddeenergization of the electrodes [9 and 20. The timing means 60 maycomprise a grid controlled gaseous discharge device 62, disposed to berendered conductive for eiiecting the energization of theoperating'winding 64 of an auxiliary switch 66, which controls theoperation of the line switch ii. The cathode or fllament 68 of thegaseous discharge device 62 is preferably connected for energization toa portion 68 of the secondary winding of a control transfer Hi, theprimary winding 12 or which may be connected to the source Hby-c0ndllct0rs 13 and 14. By connecting the operating winding 64 of theauxiliary switch 66 in series circuit relation with the anode 16 of thegaseous discharge device, an ad ditional portion ll of the controltransformer secondary winding, and the cathode 68, operation of theauxiliary switch 66 may be eifected when the gaseous discharge device 82is rendered conductive, thus connecting the operating winding 18 of theline switch IE to the source.

The conductivity of the gaseous discharge device 62 may be controlled,in a manner well known in the art, by controlling the polarity of thegrid 8| thereof. A condenser 83 may be normally connected in seriescircuit relation with a unidirectional current device, such as thecopperoxide disc rectifier 84, and a variable control resistor 86 to aportion 88 of the control transformer secondary winding, so it may becharged to any suitable potential. By subsequently e1- iecting itsconnection in series circuit relation with a current limiting resistor88 to the grid ll of the gaseous discharge device I by a grid controlrelay 80, a suitable positive bias poten-, tial may be impressed uponthe grid 8i to render the gaseous discharge device 62 conductive. Ashunt connected resistor 92 may be provided ior ensuring discharge oi.the condenser 83 when welding operations are finished. Dischargresistors 93 and 84, disposed to be connected in shunt with. thecondenser 83 upon operation of the grid control relay 90 may be utilizedfor controlling the rate of discharge oi the condenser ll, thuscontrolling the period of conductivity of the gaseous discharge device02, and the duration of the welding period. A condenser I, connected inseries circuit relation with a rectifier device ll across a portion orthe transformer winding 88, may be provided for ensuring a sharp cut-oi!o! the gaseous discharge device 62 when the bias potential of thecondenser 83 reaches a predetermined minimum value, by impressing anegative bias voltage thereon. A control resistor 91 of suitable valuemay be connected between the anode I6 and the grounded side of thetransformer winding 18 for applying an alternating current ripplevoltage to the operating winding 88 of the grid relay to prevent anytendency of the relay to seal in when the current passed by the gaseousdischarge device 62 has reached a predetermined minimum value.

In order to control the sequence of the application of electrode pressurto the work 22 and the energization of the welding circuit, diflerentialfluid pressure relays 99 and I0! may be provided. These relays aredisposed to be connected, respectively, between the source of fluidpressure 30 and the ends of the cylinder 26 of the fluid pressureactuating means. The relays may be 01 any suitable construction so as tooperate in response to predetermined differences in fluid pressurebetween the source 30 and the respective ends of the cylinder 26, andmay, for example, comprise a pair of cylinders having operativelyconnected piston members positioned therein, which are disposed to beactuated by fluid pressure. In a preferred form such relays may comprisea single cylinder with stepped bore portions I02 and Hit, havingdiameters of a predetermined ratio and having piston members I" and H18slidably disposed in the respective stepped bore portions thereof. Asshown, the piston I06, which is positioned in the upper bore portion ID!of the cylinder, may be provided with a flange Ill! about the upper edgethereof disposed to seat upon the oflset rim portion H2 0! the uppercylinder wall when the piston is in deenergized position, and extenddown into the enlarged lower bore portion I. Piston Ill may beadjustably positioned in the lower bore portion I04 of the relay by anadjusting screw Ill, so as to provide a clearance between th two pistonswhen they are in the deenergized position. A breather port I I6 may beprovided in the wall of the relay for permitting the ready entrance 0!air to the clearance space between the pistons. to prevent the formationoi an air pocket between the pistons, so that when a suitablediflerential in fluid pressure exists between th fluid pressures appliedto the upper and lower bore portions, the lower piston member I will beurged against the upper piston I" to eiiect the movement thereof. Byproviding the flange III on the piston IN, the effective upper surfac ofthe piston I06 is reduced immediately p n actuation of the piston,giving a snap" action to the movement thereof when the diflerencebetween the fluid pressure in the upper and lower bore portions of thecylinder reaches a predetermined minimum value.

The lower bore portion I of the diflerential pressure relay I may beconnected to the lower end of the cylinder 28 of the electrode fluidpressure actuating means by a suitable conduit Ill, and the upper boreportion ill of said relay may be connected to the fluid pressure sourceII by a conduit i it. Contact members lflla may be operatively connectedby the piston ill of the relay Ill for connecting the operating windingll of the grid control relay '0 acrou the portion II of the controltransformer secondary winding, so as to eilect actuation oi the gridcontrol relay SI to initiate energization of the electrodes I I and 20of the welding machin when a predetermined differential in pressureexists between the fluid pressure source 30 and the lower end of thecylinder 26 of the fluid pressure actuating means. By likewiseconnecting the lower bore portion I04 of the differential pressure relay99 through a conduit I22 to the upper end of the cylinder 26 of thefluid pressure electrode actuating means, and the upper bore portion I02thereof through a conduit I24 to the fluid pressure source 30, andproviding contact members 99a and 99b, operatively connected with thepiston I06 thereof. the operating winding I26 of an auxiliary lockingrelay I28 may be connected to a suitable direct-current source such asthe rectifier circuit I30 which is connected with thealternating-current source I4, and the operating winding 53 of the fluidpressure valve 28 and the operating winding I32 of an auxiliary relayI34 may be connected to the source I4 so as to coordinate actuation ofthese control relays with the application of fluid pressure to theelectrode actuating means.

In order to vary the interval of the ofi" period between successivewelding operations when repeat operations are being performed, asuitable check valve I35 and an associated adjustable by-pass I36 may beprovided in connection with the conduit I22 for varying the rate of flowof pressure fluid to the relay 99 from the cylinder 26, thus controllingthe duration of the oi? period, as will be hereinafter explained.

A control switch, such as the push button switch I31, may be providedfor initiating a sequence of welding operations, and an auxiliarycontrol switch I38 may be connected for shunting the contact members 99bof the differential pressure relay 99 to provide for non-repeatoperations of the welding control. dental termination of a weldingoperation through opening of the push button switch I31, the contactmembers I28i1 of the auxiliary locking relay I28 are connected in shuntrelation with the push button switch I31 to provide a shunt holdingcircuit for the operating winding 53 of the fluid pressure valve 28.

A locking relay I40, having an operating winding I42 connected acrossthe primary'winding I2 of the welding transformer I0, maybe provided formaintaining an energizing circuit for the operating winding 53 of thefluid pressure valve 28 while the welding transformer I is energized. Inorder to ensure that the energizing circuit for the operating winding 53of the fluid pressure valve 28 is properly maintained until the weldingcircuit is energized, a condenser I45 is provided in shunt circuitrelation with the operating winding I26 of the auxiliary locking relayI28 so that the energy therefrom may be utilized to maintain Suitabletime delay means I54 may be provided for retarding the operation of theprotective relay I50 so as to prevent the opening of th contact membersI50a until the lapse of a predetermined interval of time. A controlrelay I58, which is controlled thereby, is provided for efiectingdeenergization of the line switch I6 and the control circuit in general.Thus, if for any In order to prevent accireason the welding current ismaintained for too long a period, the protective relay I50 operates,effecting deenergization of the welding circuit and the control circuitso that the operating winding 53 of the fluid pressure relay 28 isdeenergized, reducing the pressure applied to the electrodes I9 and 20.

When the welding system is connected to the source I4, the control relayI58 is energized from the source through the contact members I50a of theprotective relay I50, and the control system is then in order foroperation. To initiate a single welding operation, the auxiliary controlswitch I38 and the push button switch I31 are closed, connecting theoperating winding 53 of the fluid pressure valve 28 and the operatingwinding I32 of the auxiliary relay I34 to the source I4 through thecircuit; from the source I4, through conductor 13, conductor I60,contact members I58a, push button switch I31, auxiliary control switchI38 or contact members 99b, conductor I6 I operating winding 53,operating winding I32, conductor I62, and conductor 14 back to thesource. Operation of the fluid pressure valve 28 admits fluid pressureto the lower end of the cylinder 26 of the electrode actuating meansthrough the inlet chamber 32, valve member 49, chamber 38, and conduit42 to the lower side of the piston 24, causing the electrode 20 to bemoved into engagement with the work 22. At the same time, the upper endof the cylinder 26 is connected to the atmosphere through conduit 40,chamber 36, valve member 41 and chamber 44.

The operating winding I32 of the auxiliary relay I34 being alsoenergized, contact members I34a close to connect the operating windingI26 of the auxiliary locking relay I28 to the source of direct currentI30, through conductor I64, contact members I40b of the locking relayI40, contact members 99a, conductor I65, contact members I34a of theauxiliary relay I34, operating winding I26, and conductor I61 back tothe source I30. Closure of the auxiliary locking relay contact membersI28a provides a holding circuit about the pushbutton switch I31, thusensuring an energizing circuit for the operating winding 53 of the fluidpressure valve 28 and the operating winding I32 of the auxiliary relayI34 until the locking relay I40 closes. The condenser I45 is connectedacross the operating winding I26 of the auxiliary locking relay I28through contact members I34a to ensure a momentary energizing circuittherefor, should the pushbutton switch I31 be accidentally opened beforethe locking relay I40 closes.

The reduction in fluid pressure at the upper end of the cylinder 26 alsoreduces the fluid pressure applied to the lower bore I04 of thedifferential pressure relay 99 so that the relay 99 returns to thedeenergized position and contact members 99a and 9% open when aprededetermined pressure difi'erential between the upper and lowercylinder bores thereof is attained. Likewise, the application of fluidpressure to the lower end of the cylinder 26 increases the fluidpressure applied to the lower bore I04 of the relay I00 and effectsoperation thereof when the pressure differential between the source 30and the lower end of the cylinder 2'6 reaches a predetermined minimumvalue, closing contact members I00a.

Closure of contact members I00a connects the operating winding 98 of thegrid control relay across the control transformer winding 18, effectingoperation of the grid control relay 90 to connect the grid 8I of thegaseous discharge device 82 across the positively charged con denser 83through contact members 80a. The aseous discharge device I2 is renderedconductive, energizing the operating winding 84 of the auxiliary switchI! so that the auxiliary I switch operates to connect the operatingwinding 19 oi the line switch I8 to the source through contact members66a and Inc. A shunt holding circuit for theoperating winding 94 of thegrid control relay 90 is provided by the closure oi contact members 66b.

Closure of the line switch It connects the primary winding I2 oi thewelding transformer to the source I4, energizing the electrodes I! and20. This energizes the locking relay I40, thus providing an energizingcircuit for the operating winding 53 of the fluid pressure valve 28during the welding period by providing a shunt holding circuit about thepush button switch I31 from conductor I3 through condu tor I60 contactmembers I580, contact membe I 400, conductor IBI, windings 53 and I32,conductor I82, back to conductor 14. Contact members I4Ilb oi thelocking relay I40 open, disconnecting the auxiliary locking relay I28from the direct-current source I30, and contact members I40a close toensure discharge of the condenser I45.

The duration of closure of the line switch Il may be determined by therate of discharge of the condenser 83 which applies the positive biaspotential to the grid 8| of the gaseousdischarge device 82. By varyingthe setting of the variable discharge resistor 94, this time may becontrolled over a wide range. When the bias potential falls below apredetermined level, the discharge device 82 ceases to conduct, and theoperating winding 64 of the auxiliary switch 68 is deenergized. Contactmembers 680 open, deenergizing the operat winding 19 of the line switchI, which opens and disconnects the welding electrodes I9 and 20 from thesource I4. The locking relay I40, which is connected across the primarywinding of the transformer I4 is then deenergized.

If the pushbutton switch I3! is held closed, the welding sequence cannotbe repeated for the energizing circuit for the operating winding I2 oithe relay 2! is maintained through push button switch I31 and theauxiliary control switch I28, so that the fluid pressure valve 28remains in the energized position, fluid pressure is still applied tohold the electrodes is and 20 in engagement, and the contact members IIlla remain closed, thus maintaining the grid control relay 80 in theenergized position. Since the condenser I! has been discharged and isdisconnected from the transformer winding 84 by the open contact membersWe oi the grid control relay DI, the gaseous discharge device 2 mustremain nonconductive, and the welding operation cannot be repeated. .7 u

If, however, the pushbutton switch I81 has been released, the opening ofthe contact members I40c oi the locking relay I40, upon thedeenergization of the welding circuit, interrupts the holding circuitfor the operating windings I22 and 52 ot the auxiliary relay I24 and thefluid pressure valve 28, respectively, and they will be deenergized. Thecontact members IlNla of the relay III! then open when the differentialin fluid pressure between the source 34 and the lower end of thecylinder 24 reaches a predetermined value, interrupting the holdingcircuit for the grid control relay ll so that the co denser 42 may beconnected through contact members Old-for recharging. The diiierentialpressure relay 9! is actuated to the operative position when theapplication 0! fluid presure to the cylinder 26 to separate theelectrodes II and 20 reduces the diflerential in pressures between thesource and the upper end oi the cylinder 28 to a predetermined value. Assoon as the ditierential pressure relay 9! reaches the operativeposition and contact members 93a and "b are closed, the welding sequencemay be repeated as hereinbefore described, upon subsequent closure ofthe pushbutton switch I31.

In order to eflect repeat" operations of the welding apparatus, theauxiliary control switch I3! is opened and the pushbutton switch I31held closed. Operation of the system will then be substantially the sameas hereinabove described, up to and including the energization of thewelding electrodes. When the welding current ceases to flow, asdetermined by the timing means I, the locking relay I40 opens. Thecontrol switch I38 being open, the auxiliary locking relay I24 beingdisconnected from the source I30 by the opening of contact members I4llbwhen the welding circuit was energized, and the contact members 992) oithe difierential pressure relay I! having opened when the fluid pressurevalve 24 was energized to apply pressure to the electrode 2|, theopening oi contact members I400 interrupts the energizing circuit of theauxiliary relay I34 and the fluid pressure valve 28. Upon thedeenergization of the operating winding 53 of the fluid pressure valve2|, the valve returns to the deenergized position and the fluid pressureapplied to the cylinder 2 is reversed to effect separation of theelectrodes I 9 and 20. The relay Ill returns to the deenergizedposition, opening contact members Illfla to effect deenergization oi thegrid control relay 96 so that the condenser 42 is connected throughcontact members 900 to the transformer winding for charging. Thediiierential pressure relay 88 operates to close contact members 99a and"b, when the pressure diflerential between the upper end 0! the cylinder2| and the source is reduced to a predetermined value, again providingan energizing circuit for the operating windings oi the auxiliary relayI24 and the fluid pressure relay 24, respectively, from the source I4,through conductor II, conductor Ill,

contact members Iila, pushbutton switch Ill, contact members "b,conductor III, operating windings 53 and I32, and conductor I 62, backto the source. The sequence 0! welding operations will then continue torepeat as long as the pushbutton switch I3l is held closed.

From the above description, taken in connection with the accompanyingdrawing, it may be seen that I have provided a fluid pressure operatedcontrol system for spot or seam welding apparatus that is simple andeflective in its operation, and is economical to build and maintain. Byutilizing diflerential fluid pressure relays ot the type thereinindicated, which are of simple construction and are eflicient anddurable in operation, the sequence or the energization oi the weldingelectrodes and the application 0! electrode pressure therein may readilybe controlled, and the duration of the welding operatlons timed asdesired. It will be understood, however, that while my invention hasbeen described particularly in connection with the fluid pressureoperated welding apparatus shown, it is not limited to such application,and may readily be utilized in connection with welding apparatus oiother terms.

1. The combination with a welding system comprising relatively movableelectrode members, fluid pressure actuating means for effecting relativemovement of the electrode members, valve means controlling the fluidpressure actuating means, a source of welding current, switch meansoperable to connect the electrode members to the source, and controlmeans for eflecting operation oi the switch means for a predeterminedperiod, of time delay means responsive to operation of the switch meansfor greater than the predetermined period to render the switch meansinoperative, fluid pressure relay means responsive to predetermineddifierentials of fluid pressure between different points in the fluidpressure system for initiating the operation of the control means andcontrolling the operation of the valve means in a predetermined sequencein response to the fluid pressure conditions at the source and theactuating means.

2. The combination with a welding system comprising relatively movableelectrode members, a source of welding current, switch means forconnecting the electrode members to the source, control means foreffecting timed operations of the switch means, fluid pressure actuatingmeans for effecting relative movement of the electrode members, a fluidpressure system for supplying fluid pressure to the fluid pressureactuating means, and valve means operable to apply fluid pressure to theactuating means, of relay means responsive to differences of fluidpressure in the fluid pressure system between the actuating means andthe fluid pressure supply for initiating operation of the control meansto connect the electrode members to the source in a predeterminedsequence relative to application of fluid pressure to the actuatingmeans, means responsive to the connection of the electrode members tothe source for maintaining the valve means in the operated position, andadditional relay means responsive to differences of fluid pressurebetween the actuating means and the fluid pressure supply forcontrolling the operation of the valve means.

3. The combination with a welding system comprising relatively movableelectrode members, switch means operable to control the energization ofthe electrode members from a source of ,welding current, fluid pressureactuating means for eiiecting relative movement of the electrodemembers, and valve means for connecting the fluid pressure means to asource of fluid pressure, of timing means for effecting a single timedoperation of the switch means, relay means responsive to predeterminedfluid pressure conditions at the actuating means and the source of fluidpressure for initiating the operation of the timing means in a definitesequence relative to the operation of the electrode members, and relaymeans responsive to the energization of the electrode members forpreventing operation of the valve means to disconnect the fluid pressuremeans from the source while the electrode members are energized,

4. A control system for welding apparatus having a pair of relativelymovable electrode members, switch means for controlling the energizationof the electrode members from a source of welding current, fluidpressure actuating means for efiecting relative movement of theelectrode members, fluid pressure valve means operable to control theapplication of fluid pressure to the electrode actuating means from asource of fluid pressure, comprising meansfor initiating operation ofsaid valve means, fluid pressure differential relay means forcontrolling the operation of said valve means, timing means forcontrolling the operation of the switch means, additional fluid pressurediflerential relay means for initiating operation of the timing means,relay means operable from a direct current source to ensure energizationof the fluid pressure valve means, condenser means associated with therelay means for momentarily ensuring energization thereof, andadditional relay means operable to maintain an energizing circuit formaintaining the valve means in the operated position during a weldingoperation, said fluid pressure differential relay means being responsiveto predetermined differences in fluid pressure in the fluid pressuresystem to coordinate the energization and deenergization of theelectrode members with predetermined conditions of electrode pressure.

5. The combination with a welding system having a pair of relativelymovable electrode members, a fluid pressure actuating means foreffecting relative movement of the electrode members, switch means foreffecting energization of the electrode members from a source of weldingcurrent, and a fluid pressure valve for controlling the application offluid pressure to the actuating means, of means for initiating a weldingsequence by effecting actuation of the fluid pressure valve, relay meansoperable to provide a holding circuit for the fluid pressure valve,means responsive to the energization of the electrode members formaintaining the fluid pressure valve in the ac-'- tuated position,condenser means associated with the relay means for momentarilymaintaining the relay means in the energized position, and fluidpressure means responsive to difierences in fluid pressure between theactuating means and the source of fluid pressure for controlling theoperation of the switch means in accordance with predeterminedconditions of electrode pressure.

6. A sequence control system for apparatus having relatively movablework engaging members, switch means for controlling the energization ofthe work engaging members from a source of current, fluid pressureactuating means for eflecting relative movement of the work engagingmembers, and valve means operable to connect the actuating means to asource of fluid pressure comprising, timing means for effecting a singletimed operation of the switch means,

fluid pressure relay means responsive to predetermined differences influid pressure between the actuating means and the source forcontrolling the operation of the valve means to connect the actuatingmeans to the source of fluid pressure and initiation of the timingmeans, switch means for initiating operation of the valve means,auxiliary control means including a relay having an operating windingand a condenser connected thereto to provide for maintaining the valvein the operated position, and manually operable switch meansprepositioned to control the operation of the valve means forselectively eflecting either a single or repeated welding operation.

7. A control system for apparatus having relatively movable workengaging members, fluid pressure actuating means operatively connectedwith the work engaging members, and electroresponsive valve means forconnecting the actuating means to a source or fluid pressure comprising,means for connecting the work engaging members to a source of current,timing means for controlling the operation of said means, fluid pressurerelay means responsive to predetermined fluid pressure conditions at theactuating means and the source or fluid pressure for controlling thevalve means and the timing means, and relay means responsive to theenergization of the work engaging members for preventing operation ofthe valve means to disconnect the actuating means from the source offluid pressure while the work engaging members are energized.

8. The combination with apparatus having relatively movable workengaging members, fluid pressure actuating means for effecting relativemovement of the work engaging members, and valve means operable toconnect the actuating means to a source of fluid pressure, of controlmeans comprising, means eflecting the energization of the work-engagingmembers from a source of current, a timing circuit for efiecting asingle timed operation of the said means, switch means diiierentiallyresponsive to fluid pressure conditions at the actuating means and atthe source of fluid pressure for initiating the energization of thetiming circuit, control means responsive to the energization of thework-engaging members for maintaining the valve means in the 0peratedposition, and diflerentially responsive fluid pressure relay meanscontrolling the operation of the valve means to prevent a subsequentoperation or the actuating means for a predetermined interval of time.

9. A sequence control system for apparatus having fluid pressureactuating means, an associated work circuit and valve means forconnecting the actuating means to a source of fluid pressure comprising,switch means operable to efl'ect the energization of the work circuitfrom a source of current, timing means for eflecting a single timedoperation of the said switch means. fluid pressure relay means forinitiating the operation of the timing means in accordance withpredetermined relative pressure conditions at the actuating means andthe source of fluidpressure, time delay means responsive to theenergization of the work circuit for an interval greater than providedby the timing means for rendering said switch means inoperative andadditional fluid pressure relay means controlling the operation of thevalve means in accordance with predetermined relative pressureconditions at the actuating means and at the source of fluid pressure.

COLBY W. STEWARD.

